Hi all,
I have recently finished my first complete build which is a large X8 (approx 4kg) and pleasingly it flew pretty well right from the start with default PIDs. I am running all the latest non beta software versions and have completed all the set-up apart from getting the PIDs just right. Default is OK but is all a bit sluggish and so struggles to respond quick enough during things like quick stops. I have tried an Auto Tune but that seemed to take things too far the other way and it's just really shaky in the hover. In fact, when I look at the settings that the auto tune came up with, some of them are outside of the recommended rages and mission planner pops up with a warning.
I am happy to start manually sorting out the PIDs next but I am just wondering if this is normal that the AutoTune messes things up sometimes? I understood that it was supposed to be pretty good now? This therefore leads me to be slightly concerned that there is something else wrong. Any thoughts?
Vibrations all seem ok, the battery (1kg) is under the copter and is mounted on 4 of those rubber mounts. CofG and centre of lift are as close as I can get to the same place, the FC is in the centre of the frame, blades well balanced.
thanks!
Replies
Rotorhead,
There are plenty of other variables that could be wrong. A great place to start would be to post your .bin file from a flight so that others can view the in flight data and provide feedback. Flights where autotune is performed have additional data that can be viewed and given your topic would be benificial.
Looking at your PID values those appear to be within the realm of reason. Min / Max values from my understanding are guidelines not hard n fast rules. I have several copters that fly well with Stab P/R values of 15+
There are settings in the full parameter listing that apply to how aggressive an autotune is and the responsiveness of the copter post autotune. for example some of the ATC_Accell parameters directly relate to how quickly a multi responds to PILOT INPUTS. It is advisable to lower these before lowering any rate or stability value.
A good starting point is to pull into a hover post autotune and IF without any input from you the multi is not twitching your autotune is probably fairly good. Try lowering RC_Feel first and then ATC_Accel next. You will find that twitching in response to pilot input could be because you are exceeding the rate of response your copter can produce.
I have done exactly the above process and a copter that was twichy when i moved it around is now stable and flies incredibly well.
Autotune with Agg set to .05 vice the default of .1 will also yield a better result for some (not sure if this is a pre-3.3Rc8 feature. It has been a while since i've used 3.2.) Feel free to try the beta version as well as the 3.3beta testing thread covers extensive details regarding autotune and throttle to voltage compensation settings.
Ssome of the new features are priceless to me and despite it being called Beta i find it is a significant improvement over 3.2. Feel free to read the thread and see if its for you. If not 3.2 can be adjusted all the same with a few parameter tweaks.
Brilliant info, thanks for your time there! I will get out as soon as I can and get another autotune done so I can post the log. Weather and work getting in the way just at the mo however!
The problematic twitching I had after the autotune was in the hover with no contoller input and in all flight modes. It's just a very high frequency oscillation in roll.
When i first flew Pixhawk i though my Hex was fine on the standard settings but thought Autotune would make it better.
It was impossible to fly and i returned to standard, luckily had taken note of the parameters.
Symptoms were, while still on the ground it would shake madly as i built the revs trying to lift off. Violently shaking i mean.
Not tried Autotune since.
What exactly is wrong ? , what parameter(s) do you need to correct later ?
I have seen STB_*_P are often much too high, after autotune
I am not sure which ones are wrong, I just know that it flies better before the tune. The ones that are supposedly outside the limits are the rate PIT P and rate RLL P. I have messed with reducing STAB Roll and Pitch P back to the default but it still has the twitch. I'll try and get one of the logs from one of the auto tunes but I don't know when it was now. I might just have to do another and then post it.
I have included a table of the default params and then the autotuned params below. I'm not sure if it will keep it's formatting though: